Potential of wax degrading bacteria for management of the citrus mealybug, Planococcus citri

The efficiency of four species of wax degrading bacteria, Serratia marcescens (Bizio) (Enterobacterales:Yersiniaceae), Pseudomonas putida (Trevisan) (Pseudomonadales: Pseudomonadaceae), Bacillus subtilis (Ehrenberg) (Bacillales:Bacillaceae) and Bacillus cereus (Frankland & Frankland) (Bacillales:Bacillaceae) for the management of a major citrus pest, the mealybug, Planococcus citri (Green) (Hemiptera:Pseudococcidae) was evaluated. The degrading ability of the bacteria, isolated from cadavers of P. citri was assessed in vitro on wax extracted from the mealybug, paraffin wax and low-density polyfilm along with lipase activity. Except B. cereus, all bacteria showed significant lethal and debilitating effects against P. citri in laboratory bioassays. Even though, we did not observe any lethal effect on 1st and 2nd instar nymphs, in the latter instars mortality rate could reach as high as 70.0% in case of S. marcescens. Adults that survived bacterial treatments had significantly reduced female longevity, fecundity and adult formation. In greenhouse trail conducted under controlled conditions, it was found that S. marcescens was the most promising bacteria in managing P. citri population after 14 days of application causing around 36.5% mortality of crawlers coupled with a significant reduction in the wax content and weight of mealybug. However, its application followed by a single spray of half a dose of chlorpyrifos at weekly intervals further enhanced the mortality rate up to 54.0%. Therefore, we conclude that sequential application of S. marcescens followed by a single spray of a half a dose of insecticide is effective for management of the P. citri.